The long-term goal of this research is to understand how changes in properties of neurons lead to the formation of memory and subsequent changes in behavior. The behavioral framework of our research is long-term sensitization of the defensive tail, siphon withdrawal reflex of Aplysia. Glutamatergic sensory neurons are key components of the reflex. Long-term presynaptic facilitation (LTF) at the sensory-motor synapse is mainly responsible for sensitization. We hypothesize that a number of properties of a sensory neuron must change in a coordinated fashion to produce LTF and store memory. Thus, we predict that the increase in transmitter release that occurs during LTF should be coordinated with an increase in uptake and synthesis of glutamate. In testing this hypothesis, we found that sensitization training leads to a substantial long-term increase in the Vmax of the high affinity neuronal glutamate transporter. In addition, we found that glutamine uptake was increased suggesting that glutamate synthesis was also increased. These findings provide the basis for molecular and biochemical studies on newly-discovered plastic properties of the sensory neuron. In particular, we will study molecular correlates of memory storage and expression in Aplysia and will extend these findings to research on long-term potentiation in the hippocampus of rats. The proposed research has 4 Specific Aims: Aim 1 is to determine the relationship between increases in glutamate uptake, glutamate synthesis, and behavioral sensitization. Aim 2 is to determine the cellular mechanisms that mediate coordinate regulation of glutamate uptake, synthesis, and long-term facilitation. Aim 3 is to determine whether the mechanisms responsible for the long-term increase in glutamate uptake involve synthesis of transporters and then transport through the ER-Golgi-vesicle transport pathway. Aim 4 is to determine the generality of regulation of uptake by studying glutamate uptake during long-term potentiation in the CA1 region of the hippocampus. Deficiencies in glutamate uptake have been implicated in a number of diseases (e.g., ALS, Hodgkin's, Alzheimer's). Glutamate appears to be a remarkably potent and rapidly-acting neurotoxin. This underlines the important role of glutamate uptake in the normal functioning of brains. Our research will help elucidate possible causes for decreased glutamate uptake in these diseases by identifying mechanisms responsible for long-term regulation of glutamate transporters.